to get you guys up to speed, I posted this last December
https://www.ford-trucks.com/forums/5...8f150-4wd.html

Since then, I've not only replaced the Calipers/brakes, but also every single brake line is now brand new as well. Last week I bought a new Master Cylinder as well as the lines down to the Valve and put that on. With the new MC, the problem has actually GOTTEN WORSE!

the only way I can release the pressure from brakes is to crack the bleeder screws and watch the fluid shoot like Peter North.

Many people have told me that there is no way that it can be the Proportion Valve, but I dont see what else could cause such pressure buildup and lack of fluid release off the rotors.

Also, I noticed there is some electrical involved in the Valve. If I buy a new one, will that come as well? Maybe that is the damaged part.

 

did you replace the rubber brake hoses? check the brake booster also if the pedal stays down, if the old master leaked. the master probably leaked fluid into the booster and it will freeze the pedal down. you maybe able to pull it up. the brake hoses can collapse inside. fluid may go in, but not be able to flow back through.

 

check also make sure the pads wear evenly. the slides on my 77 did not work, and wore out a relatively new rotor and blew the pads out. i am doing the same all brakes and lines metal and rubber are getting done on mine. calipers, wheel cylinders, master and rotors. drums are still good.

 

my wife HATES my truck. i spend alot of time with it. i told her i could have spent 2500 on a truck and 6 month down the road be doing the same. she has learned to realize that i love my old trucks. i always get my money out of them.

 

i also had this problem on an old buick and it turned out to be both rubber hose that bolt to the calipers but youre truck as 33" tire maybe a lift and maybe you have stainless steel flexible brake lines not installed proprely...?check that out!

 

Low Brake Fluid Warning Light Switch ~ It doesn't come with the valve, it's sold by itself.

C8AZ-2B264-A .. Switch, Low Brake Fluid Warning Light

 

The problem with posting a new thread instead of updating the old one is people don't know what has already been said and done... so some things get repeated.

Here is the original thread so people can go thru it and see what has been suggested already.

https://www.ford-trucks.com/forums/5...8f150-4wd.html

Maybe a Mod will merge them for him ?

 

Dennis, I put the old thread in my first message. Looks like a few people didnt pick that up. Ive replaced ALL the brake lines, Calipers, brake pads, and now the Master Cylinder. The pressure is just not releasing from the pads once the braking system gets warmed up a little and so the brakes get 75% engaged and there is no play in the pedal. it is stiff right at the top.
I just feel that is has to be the Valve at this point. Unless someone has another idea I will look into the best place to get a new one this week and have it on soon

 

I missed it as well.

Have you physically turned both rotors by hand once the brake pedal is released?

Ford disc brakes are knwn as "constant rub" as they only pull away a minute fraction after the pedal is released.

 

Is the shaft on the booster too long? Some of the rigs I've worked on have an adjustment to the shaft where the booster contacts the m/c. Is there any freeplay on the brake pedal? Your pedal would keep the pressure in the system if it was applying pressure to the system from lack of freeplay.

Apply the brakes and get the trapped pressure you discribed, then try unbolting the m/c from the booster and see what happens, of course don't crack the lines. Should tell you wether its a mechanical or hyd problem.

 

You can see the booster pushrod measurement here on one of my pages.

http://www.clubfte.com/users/mil1ion...trations2.html

 

Yeah, Ive heard of that booster pushrod adjustment. I'll obviously check that out tommorrow before I buy a new Valve.

One question--Lets say that the rod is out too far, in effect keeping the Master Cylinder partially engaged.

Wouldnt that also let the fluid flow back into the MC just as easily, thereby releasing the pressure?

 

Not if the cups are expanded in the bore from not being able to return all the way. Residual pressure in the MC would keep the rubber cups expanded. If the rotors are dragging that will generate heat, causing the fluid to expand. If there is no where for the fluid to go it'll build pressure and lock the brakes up since tightening the caliper is the only way for expansion in the hyd circuit.

Just a theory.

 

You're gettin a little over my head, chief. Basically you are saying to just take of the MC and spin the pushrod around a little until the MC sits flush on the booster without touching the rod?

Am I gettin it right?

 

if the booster rod isnt proprely ajusted unbolt the master cyl. pry it forward out of the stud so the booster rod wont touch the m.c. then check if your wheel are turning free.
if yes then put the master back on and check if your wheel are not turning.